1. Field of the Invention
The present invention relates to an inkjet printing apparatus and a predicting method of predicting an ejecting state of ink of a print head.
2. Description of the Related Art
In recent years, in a printing apparatus such as a printer, a copying machine, a facsimile device or the like, an inkjet system capable of ejecting a minute ink droplet with a high frequency becomes widely used. Among others, a printing apparatus of a thermal inkjet printing system for ejecting ink by using bubbles generated by driving a heater (electrothermal converter or energy generating element) can form highly concentrated nozzles to print an image in a highly fine quality.
The inkjet printing apparatus is generally used in such a manner that an ink tank filled with ink is mounted and when the ink tank becomes empty by printing, the ink tank is replaced. Some of this type of printing apparatuses, for preventing ink from running out during printing, have a function of informing a user whether or not the ink runs out by detecting an ink remaining amount before printing. Particularly, in the equipment where print data such as facsimiles are not left in a user's side, a high detection accuracy of the ink remaining amount is required for preventing empty printing that the ink is not ejected due to the running-out of ink.
As a method of determining an ink remaining amount, there is known a method of detecting an ink remaining amount based upon an ink use amount obtained by counting the number of the times of ink ejections from a point where an ink tank is not used or a method of detecting an ink remaining amount by emitting light on an optical transmission portion of an ink tank.
Moreover, there is known a method of determining an ink remaining amount by detecting a change in print head temperature before and after driving a heater. In a case of driving the heater in a state where ink exists sufficiently in an ink tank, since the ink heated by the heater foams and ejects to consume the energy, heat is not relatively stored in the print head. On the other hand, in a state where the ink tank is empty due to non-existence of the ink, since the heat generated by driving the heater all is stored in the print head, a temperature in the print head is high. In a method of determining an ink remaining amount by detecting a temperature change of the print head, the ink remaining amount is determined using such a phenomenon. Since in this method, it is determined whether or not the ink is actually ejected, an accuracy of detecting a remaining amount immediately before the ink runs out is high.
In a technology disclosed in Japanese Patent Laid-Open No. H06-336024(1994), a monitor value of the print head temperature is compared with a prediction value of a print head temperature led from energy inputted to the print head, and presence/absence of ink is determined by comparing the above comparison result with a predetermined threshold value. With use of this method, the heater drive can be stopped in a point where the ink ejection can not be carried out from all nozzles from a point where the ink ejection is started. Therefore, the ink is not wastefully consumed unlike a case of driving the heater in a predetermined time. Further, since an empty ejection of continuing to drive the heater in a state where the ink runs out is not also carried out, the print head does not have a temperature higher than necessary. Therefore, the print head endurance also improves.
The print head temperature, however, changes with a head temperature immediately before driving the heater, an atmosphere temperature at that time or the like. Accordingly, in a case of detecting an ink remaining amount immediately after the completing printing, an accurate temperature of the print head can not be possibly detected due to a rise of the head temperature by the printing. That is, the print head temperature detection at the time of detecting the ink remaining amount results in being performed in a state where the print head temperature is unstable, and therefore, the monitor value and the prediction value of the print head temperature may not be obtained accurately and stably.